Having trouble with an unexpected value in your Angular2 Service? Don't forget to add

I encountered an error in my Angular2 app: Error: (SystemJS) Unexpected value 'ReleasesService' declared by the module 'AppModule'. Please add a @Pipe/@Directive/@Component annotation.

Here is my AppModule code:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { routing } from './app.routes';
import { HttpModule } from '@angular/http';
import { SearchFilter } from '../app/search-filter.pipe';
import { ReleasesService } from '../app/releases/releases.service';
import { AppComponent }  from './app.component';
import { HomeComponent } from '../app/home/home.component';
import { ReleasesComponent } from '../app/releases/releases.component';
import { DistroComponent } from '../app/distro/distro.component';
import { ContactComponent } from '../app/contact/contact.component';

@NgModule({
  imports:      [ BrowserModule, HttpModule, routing ],
  declarations: [ AppComponent, 
                  SearchFilter,
                  HomeComponent, 
                  ReleasesComponent, 
                  ReleasesService,
                  DistroComponent, 
                  ContactComponent  ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

This is my ReleasesService code:

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import { IRelease } from './release';
import 'rxjs/add/operator/map';

@Injectable()
export class ReleasesService {
  getReleases() {
    return IRelease;
  }
}

How can I resolve this issue? I have tried reinstalling the Quickstarter, which serves as the foundation for my app, but still encounter the same error when attempting to create the service.

Answer №1

declarations is specifically meant for declarable classes like Components, Directives, and Pipes

If you want to use the ReleasesService, make sure to add it to the providers array in your Angular module

@NgModule({
  imports:      [ BrowserModule ],
  declarations: [ AppComponent ],
  providers:    [ ReleasesService ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

For more information, check out:

Answer №2

Dealing with a similar issue myself, I encountered an issue when one project had angular2 as a dependency and another project had a dependency (containing the problematic component) as well. It seems that angular2 metadata becomes attached to the primary angular2 dependency, causing the component in the secondary project's dependency not to be declared within the main project's angular2 scope.

A workaround I discovered was removing angular2 from the secondary dependency (declaring it as a devDependency instead) and utilizing only a single instance of angular2 for better compatibility.

Answer №3

It is important to include the "@" symbol before using a decorator.

If you forget to add "@" before the decorator function, you will encounter the following error message:

@Component({ selector: '...', }) -> Correct

Component({ selector: '...', }) -> ERROR MESSAGE: 'add a @Pipe/@Directive/@component'

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